Redesigned fuel tank lets lawn mower stand upright

By: Kerri Jansen

May 9, 2014

Small-engine maker Briggs & Stratton Corp. has unveiled a new lawn mower engine that allows a gas-powered mower to be stored upright without leaking, thanks in part to a carefully engineered fuel tank.

Looking to create a space-saving storage option while maintaining cutting power, engineers developed engine components that can be safely rotated 110 degrees.

“We were looking for ways to bring some innovation to the lawn and garden market,” said Steve Lavender, senior director of engineering at Briggs & Stratton. “One of the issues was the whole idea of how much room a mower takes in the garage, and it would take up less room if you stood it up on end.”

Engineers faced the challenge of containing fuel and oil when the engine is in a vertical position. Fluids can leak from air vents and any seals, like the one around the fuel cap.

“When you think about servicing a lawn mower you have to be careful, even when you’re changing the blade, which direction you tip the mower so you don’t spill gasoline. So this really for us, it came out of a greater focus on innovation,” Lavender said.

Fuel tanks are designed to trap a volume of air so gasoline has room to expand with increased temperature. The fuel tank used with the Mow ‘n’ Stow engine is L-shaped so that when the mower deck is rolled into a vertical position, even a full fuel level is contained below the level of the fuel cap.

“The air that was above the volume of fuel moves to being where the gas cap is, so the gas cap stays above the fuel capacity of the tank,” Lavender said.

The tanks are made from a type of nylon 6 with low permeation, to meet guidelines on evaporative emissions, Lavender said. Popular fuel tank material high density polyethylene is permeable as a single layer and allows vapors to escape the tank via evaporation. Swapping HDPE for nylon 6 allows Briggs & Stratton to use a monolayer tank, rather than a multilayer one.

Tanks for Mow ‘n’ Stow engines are injection molded in two halves by a supplier in Missouri, Lavender said.

Engineers also moved vents on the carburetor and improved the seal on the engine’s oil fill tube to prevent leakage. Briggs & Stratton partnered with lawn equipment provider Toro Co. to bring the engine to market, in the form of Toro’s self-propelled Recycler with SmartStow, which is in stores now. The engine will also likely appear in future models currently in development, Lavender said.